Electrophysiological experiments will be performed on sympathetic neurons dissociated from the superior cervical ganglia of newborn rats and grown in cell culture. In these experiments microelectrode techniques will be used to investigate several electrophysio-logical properties of the sympathetic neurons developing in culture. These properties will include (a) the contributions of sodium and calcium in the action potential mechanism; (b) the ionic mechanism responsible for a long after hyperpolarization which follows the action potential and which appears to develop in these neurons in culture; (c) the presence of delayed rectification; (d) the ability of the neurons to repetitively produce action potentials to a steady maintained depolarization (accommodation); and (e) acetylcholine noise fluctuations. Membrane noise characteristics will be analyzed by use of fluctuation analysis and statistical properties computed using the Fast Fourier Transform on a digital computer. The major objectives of the research are 1) to use these properties to characterize as quantitatively as possible the electrophysiological development of sympathetic neurons grown in culture in the absence of other cell types; and (2) to determine in what way and to what extent these properties are influenced by the presence in the culture of other dissociated cell types such as cardiac or smooth muscle (which are potential target cells), skeletal muscle, spinal cord (presynaptic neurons), fibroblasts, or glia. In this way influences of cellular associations which affect the electrophysiological development of sympathetic neurons and which would otherwise be difficult or impossible to detect in vivo, might be uncovered.